I'm not sure if you are aware of this or not, but there is a website called
TwistedRoad that lets you rent other people's motorcycles. It's more expensive than a rental car, but much cheaper than buying two extra motorcycles in a year. Selection is kinda limited, but if there is a major city near you, I bet you can find a triple and a 6 cylinder. Goldwings are pretty popular. I bet you can find an MT09 or one of Triumph's many triples there too.
No, I'm not affiliated with TwistedRoad in any way. It just happens to be a website I've considered using before. I bet there are others too.